JPH06190856A - Foam injection molding method - Google Patents

Abstract

(57) [Summary] [Purpose] Mold inexpensively a foam-molded product that is free from sink marks and has a better appearance quality. [Structure] The amount of shearing heat generated in the molten resin is reduced by adjusting the valve opening of a rotary valve 20 for the molten resin added with a foaming agent from the cylinder 15 into the cavity 12 of the mold 12. The molten resin is controlled to be injected and filled in the cavity 18 by controlling the opening of the rotary valve 20 to increase the amount of shearing heat generated in the molten resin. After the injection and filling, the molten resin is further injected and filled into the cavity 18 by controlling the opening degree of the rotary valve 20 so as to reduce the amount of shearing heat generated in the molten resin. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam injection molding method applied to molding a foam molded article.

[0002]

2. Description of the Related Art Conventionally, foam molded articles have been widely used as TV cabinets, OA equipment housings, automobile interior and exterior parts, furniture and the like. The following molding methods are known as molding methods for this foamed molded product. (1) A molding method in which a molten resin added with a foaming agent in an injection unit is heated to a temperature equal to or higher than a decomposition start temperature of the foaming agent, and the heated molten resin is injected and filled into a cavity of a mold ( Foam injection molding: Takashi Mori "Introduction to plastic molding" (1985-5-20) Industrial Research Group p.63-64). (2) Using an injection molding machine equipped with two injection units,
The molten resin to which no blowing agent is added (molten resin without blowing agent) is accumulated in one injection unit, and the molten resin to which the blowing agent is added (molten resin with blowing agent) is accumulated in the other injection unit. Then, after heating the other injection unit to a temperature equal to or higher than the decomposition start temperature of the foaming agent, first the injection resin is filled with the foaming agent-free molten resin from the one injection unit and the foaming is performed. A surface layer (skin layer) of a molded product is formed from a non-agent-added molten resin, and then a foaming agent-added molten resin is injected and filled into the cavity from the other injection unit, and the molded product is formed from the blowing agent-added molten resin Molding method for forming the core material (sandwich molding method: "Plastic Age" 1990)
March issue, p. 161-162). According to this molding method, a dense skin layer of a molded product is formed by the foaming agent-free molten resin, and the skin layer is pressed against the inner wall surface of the mold by the foaming pressure of the foaming agent-containing molten resin that forms the core. As a result, a molded product having a good appearance without sink marks can be obtained. (3) The molten resin added with the foaming agent in the injection unit is heated to a temperature lower than the decomposition start temperature of the foaming agent, and the heated molten resin is heated by the flow path resistance provided in the melted resin supply flow path. A molding method in which the molten resin is injection-filled into the cavity of the mold while causing shearing heat generation (US Patent No.
3776989 specification). According to this molding method, the molten resin in which shearing heat is generated due to the channel resistance in the molten resin supply channel is foamed in the cavity, but the portion of the molten resin in contact with the inner wall surface of the mold is instantly Since it is solidified by cooling, it hardly foams. Therefore, since the skin layer of the molded product is formed by the molten resin that hardly foams, the molded product has a relatively good appearance. In addition, since shear heat is generated in the molten resin by the flow path resistance provided in the molten resin supply channel to foam the molten resin, the molded product can be molded at a relatively low cost.

[0003]

However, the above-mentioned molding method has the following problems. In the molding method (foam injection molding) described in (1), since the molten resin to which the foaming agent has been added is heated to a temperature above the decomposition start temperature of the foaming agent in the injection unit, As a result, foaming of the molten resin has already occurred. For this reason, this foamed molten resin is injected and filled in the cavity of the mold and appears on the surface of the molded product, and silver streaks occur on the surface of this molded product, so the surface of the molded product looks It becomes defective. Further, when appearance quality is required for this molded product, the surface of the molded product needs to be subjected to post-treatments such as polishing and painting, which inevitably results in reduced productivity and increased cost. With the molding method described in (2) (sandwich molding method), a molded product with good appearance without sink marks can be obtained, but since two injection units are required, the structure of the injection molding machine becomes complicated. At the same time, the injection molding machine becomes expensive, resulting in cost increase. (3)
In the molding method described in (1), since the skin layer is slightly foamed, the requirements for the appearance quality of the molded product cannot be sufficiently satisfied.

The present invention has been made in view of the above problems, and provides a foam injection molding method capable of inexpensively molding a foam-molded article having no appearance of sink marks or the like and having improved appearance quality. The purpose is to provide.

[0005]

In the foam injection molding method according to the present invention, first, a molten resin to which a foaming agent is added and which is melted at a temperature lower than the decomposition start temperature of the foaming agent is used as a mold. A method of foam injection molding in which the foaming agent is thermally decomposed by causing shearing heat generation in the molten resin during injection filling into the cavity of the cavity, and the heating value of the shearing heat generation is reduced at the initial stage of injection filling. It is characterized in that a step of controlling is performed, and thereafter, a step of controlling so as to increase at least the heat generation amount of the shear heat generation is performed.

Further, the foam injection molding method according to the present invention is
Secondly, when the molten resin melted at a temperature lower than the decomposition starting temperature of the foaming agent is injected and filled into the cavity of the mold, shear heat is generated in the molten resin. A foam injection molding method of thermally decomposing the foaming agent by carrying out a step of controlling to reduce the heat generation amount of the shearing heat generation at the initial stage of injection filling,
After this, at least a step of controlling to increase the heat generation amount of the shear heat generation is performed, and then a step of controlling to reduce the heat generation of the shear heat is performed at the final stage of injection filling.

The amount of heat generated by the shear heat generation is controlled by adjusting the flow passage area of the melted resin supply passage by the flow passage resistance provided in the melted resin supply passage, and when the melted resin is injected and filled into the cavity. It is better to adjust the injection pressure and the injection speed of.

[0008]

In the foaming injection molding method having the first feature of the present invention, while the foaming agent is added and the molten resin melted at a temperature lower than the decomposition start temperature of the foaming agent causes shear heat generation. When injection-filling into the cavity of the mold, a step of controlling the amount of heat generated by shearing to be small is performed in the initial stage of injection-filling. In this step, the skin layer of the molded product is formed by the molten resin, but the foaming agent is not thermally decomposed because the heat generation amount of the shearing heat generation is small, whereby the molten resin is stored in the cavity. Since it does not foam, a dense skin layer is formed. After that, a step of controlling to increase the heat generation amount of the shear heat generation is performed. In this step, since the heat generation amount of the shear heat generation is increased, the foaming agent is thermally decomposed, whereby the molten resin is foamed in the cavity, and the foamed molten resin forms the core of the molded product. To be done. In this way, a dense skin layer is formed by the molten resin that does not foam, and this skin layer is pressed against the inner wall surface of the mold by the foaming pressure of the molten resin that forms the core, so there is no sink mark, etc. It is possible to obtain a foam-molded article having improved properties. Further, after performing the step of controlling to reduce the heat generation amount of the shear heat generation, for example, a step of controlling to increase the heat generation amount of the shear heat generation or a step of controlling to increase the heat generation amount, By sequentially performing multiple times while controlling the timing,
The foamed molten resin can be made to exist in a predetermined portion of the molded product depending on the shape and use of the molded product, thereby suppressing occurrence of sink marks or the like at the predetermined portion of the molded product.

Further, in the foam injection molding method having the second feature of the present invention, the step of controlling to reduce the heat generation amount of the shear heat generation in the same manner as the foam injection molding method having the first feature. After that, at least a step of controlling to increase the heat generation amount of the shear heat generation is performed, and then a step of controlling to reduce the heat generation amount of the shear heat generation is performed at the final stage of injection filling. In the step performed at the final stage of this injection filling, the heat generation amount of the shear heat generation is made small, so that the foaming agent is not thermally decomposed, whereby the molten resin does not foam in the cavity, and the molten resin that does not foam. Thus, the foamed molten resin forming the core is covered. In this way, the foamed molten resin does not appear on the surface of the molded product, and the appearance quality of this molded product can be further improved.

By the way, the temperature rise of the molten resin due to the heat generated by shearing is generally given by the following equation. ΔT∝ΔP = f (η, r, P _i , V _i ) where ΔT: degree of temperature rise of molten resin due to heat generated by shearing ΔP: pressure loss in flow path resistance part η: viscosity of molten resin r: flow path resistance part Shape factor of P _i : Injection pressure of injection molding machine V _i : Injection speed of injection molding machine From this equation, the temperature rise of the molten resin due to shear heat generation is proportional to the pressure loss in the flow path resistance part, and this pressure loss is It can be seen that it is determined by the viscosity of the molten resin, the shape factor of the flow path resistance portion, the injection pressure of the injection molding machine, and the injection speed.
Therefore, the heat generation amount of the shear heat generation is controlled by adjusting the flow channel area of the molten resin supply flow channel by the flow channel resistance provided in the molten resin supply flow channel, and when the molten resin is injected and filled in the cavity. It is preferable to adjust the injection pressure and the injection speed.

[0011]

Next, specific examples of the foam injection molding method according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic view of an essential part of an injection molding machine to which the foam injection molding method of the present invention is applied. The injection molding machine 11 has, for example, a mold clamping force of 80 t and an injection capacity of 12
A mold 1 having a performance of 0 ml and connected to the injection molding machine body 11a and the nozzle portion 12 of the injection molding machine body 11a.
3 and 3.

The injection molding machine body 11a includes an injection unit 14
The cylinder 15 of the injection unit 14 is heated to a set temperature of 180 ° C., for example. This cylinder 1
In the upper part of 5, a blowing agent (for example, ADCA (azodicarbonamide) -based blowing agent, decomposition starting temperature: 200 ° C.)
A material hopper 16 for supplying molten resin (for example, polypropylene (J440, manufactured by Mitsui Petrochemical Co., Ltd.)) added with hr (parts per hundred parts of resin) is arranged, and the cylinder is also provided. A molten resin supply channel (hereinafter referred to as a channel) 17 is formed by kneading the molten resin into the nozzle portion 15 and punching the nozzle portion 12.
A screw 19 of, for example, a double flight type, which is injection-filled into the cavity 18 having a cavity volume corresponding to the intended volume of the molded product of the mold 13 through the above, is installed. Further, a rotary valve 20 as a flow path resistance is arranged in the nozzle portion 12, and the flow path area of the flow path 17 is changed by adjusting the valve opening degree of the rotary valve 20. The control of the valve opening of the rotary valve 20 is performed by a control device (not shown).

The base of the screw 19 is connected to a screw rotation motor 21, and the screw 19 and the screw rotation motor 21 are attached to a base 22. The base 22 is driven in the left-right direction in FIG. 1 by the drive control device 23, in other words, the screw 1 for injection filling of the molten resin into the cavity 18 and the like.
Drive control is performed for advancing and retreating the nozzle 9 toward the nozzle portion 12, and for applying a predetermined pressing force to the screw 19 for injecting and filling the molten resin in the cylinder 15 into the cavity 18 at a predetermined injection pressure and injection speed. It is performed by the device 23 through the substrate 22.

The mold 13 is composed of a fixed mold 24 joined to the nozzle portion 12, an intermediate mold 25 forming a cavity 18, and a movable mold 26. The movable mold 26
The cavity volume of the cavity 18 is expanded or contracted by moving back and forth. Reference numeral 18a in the drawing is a gate portion. This movable mold 26 is engaged with a piston rod 28 of a compression cylinder 27, and this piston rod 28 is driven in the left-right direction in FIG. 1 by a drive control device (not shown). That is, when the piston rod 28 is driven to the right, the movable mold 26 advances and the cavity volume of the cavity 18 is reduced, and when it is driven to the left, the movable mold 26 retracts and the cavity of the cavity 18 moves. The volume is expanded. The front side of the movable mold 26, that is, the intermediate mold 25.
A return pin 29 is provided on the side, and the return pin 29 comes into contact with the intermediate mold 25 when the movable mold 26 moves forward, thereby restricting the movable mold 26 from moving forward to serve as the purpose of the cavity 18. The volume of the molded product is secured. In addition, a stopper 30 is provided behind the movable mold 26.
Is provided, and when the movable die 26 comes into contact with the stopper 30 when the movable die 26 retreats, the retreat of the movable die 26 is regulated and the further expansion of the cavity volume of the cavity 18 is regulated. is doing.

The set temperature of the cylinder 15 is lower than the decomposition start temperature of the foaming agent, preferably 20 ° C. lower than the decomposition start temperature. This is because when the set temperature becomes close to the decomposition start temperature of the foaming agent, the cylinder 15
This is because the thermal decomposition of the foaming agent may proceed inside, and if the set temperature is too low, the fluidity of the molten resin will decrease.

Next, the injection molding machine 1 configured as described above.
The operation of No. 1 will be described.

(First Embodiment) In this first embodiment, shearing heat is generated by setting the injection pressure and injection speed of the injection molding machine 11 to normal injection molding conditions and adjusting the valve opening of the rotary valve 20. A case of controlling the heat generation amount of will be described.

First, by a known means, the intermediate mold 25 and the movable mold 26 are integrally brought closer to the fixed mold 24 so that the cavity volume of the cavity 18 becomes a target molded product volume. The mold of 13 is closed.

Next, while the valve opening of the rotary valve 20 is set to 100% (fully opened) by the control device, the molten resin containing the foaming agent is injected and filled from the cylinder 15 into the cavity 18. At this time, since the valve opening is set to 100%, the heat generation amount of the shearing heat generated in the molten resin in the flow path 17 is small, and the molten resin does not foam in the cavity 18. Thus, a dense skin layer of the molded product is formed by the molten resin that does not foam.

Then, the cavity 18 filled with the molten resin that does not foam is injected and filled with the molten resin from the cylinder 15 while the valve opening of the rotary valve 20 is set to, for example, 30% by the controller. At this time, since the valve opening is set to 30%,
The amount of heat generated by shearing heat generated in the molten resin in the flow path 17 increases, and the shearing heat causes the foaming agent added to the molten resin to be thermally decomposed. It foams in the cavity 18. Thus, the foamed molten resin forms the core of the molded article.

By the way, as shown in FIG. 2, such a rotary valve raises the temperature of the molten resin by causing shearing heat generation in the molten resin passing through the rotary valve according to the opening of the valve. It is what makes me.
Therefore, if the valve opening is set to, for example, 30%, the molten resin is heated by about 60 ° C. Incidentally, in such a rotary valve, the degree of temperature rise of the molten resin can be controlled within a range of, for example, about 80 ° C. by appropriately setting the valve opening degree as can be seen from FIG. The amount of heat generated by shearing heat generated in the molten resin by such a rotary valve varies depending on the type of molten resin passing through the rotary valve, the shape of the rotary valve, and so on. It is necessary to obtain data and determine the set temperature of the cylinder based on the data.

Next, the valve opening of the rotary valve 20 is again set to 100% by the control device in the cavity 18 in which the molten resin that does not foam and the foamed molten resin that forms the core are injected and filled. Then, the molten resin is further injected and filled from the cylinder 15. At this time, since the valve opening is set to 100%, the heat generation amount of the shearing heat generated in the molten resin in the flow path 17 becomes small, and the molten resin becomes the cavity 1
No foaming within 8. Thus, the molten resin that forms the core is covered with the molten resin that does not foam, and the cavity 18 is injected and filled with a volume of the molten resin that corresponds to the intended volume of the molded product.

After the molten resin in the cavity 18 is cooled and solidified, the intermediate mold 25, the movable mold 26 and the stopper 30 are separated from the fixed mold 24 by a known means to open the mold 13. After this, the piston rod 28
When the movable mold 26 is moved forward by moving the movable mold 26 to the right, the molded product made of the molten resin held in the intermediate mold 25 is projected from the back and separated from the mold 13.

A molded article (Example 1) molded by using the injection molding machine 11 in the first embodiment, and a set temperature of the cylinder 15 of the injection molding machine 11 and / or the set temperature by using the injection molding machine 11 and / or Table 1 shows the molding conditions and the evaluation results for the molded products (Comparative Examples 1, 2, 3) molded by changing the valve opening of the rotary valve 20. The arrow (→) in the valve opening degree in Table 1 indicates that the setting of the valve opening degree is changed.

[0026]

[Table 1]

As can be seen from this evaluation result, in the molded product of Example 1, the valve opening of the rotary valve 20 was set to 3
When set to 0%, the amount of heat generated by shearing heat generated in the molten resin added with the foaming agent passing through the rotary valve 20 becomes large, and the molten resin is heated to over 50 ° C. As a result, the foaming agent is thermally decomposed and the molten resin foams in the cavity 18. The molded product of this Example 1 was first manufactured by the rotary valve 2
By setting the valve opening degree of 0 to 100%, a dense skin layer is formed by the molten resin.
Since the core is formed of the molten resin by setting the valve opening of the rotary valve 20 to 30%, the skin layer is pressed against the inner wall surface of the mold 13 by the foaming pressure of the core. Then, by setting the valve opening degree of the rotary valve 20 to 100% again, the core is covered with the molten resin. Thus
It is possible to obtain a foam-molded product with improved appearance quality without sink marks, silver streaks, etc.

On the other hand, in the molded product of Comparative Example 1, since the valve opening of the rotary valve 20 is fixed at 100%, the amount of shearing heat generated in the molten resin is small and the molten resin is small. Does not foam in the cavity 18. Therefore, in this molded product, a fine skin layer without silver streaks is formed, but a sink mark is generated, so that the appearance quality is poor. Further, in the molded article of Comparative Example 2, since the set temperature of the cylinder 15 is set to 240 ° C. which is higher than the decomposition start temperature of the foaming agent, that cylinder 1
In FIG. 5, foaming of the molten resin has already occurred. Therefore, the foamed molten resin is injected and filled into the cavity 18 and appears on the surface of the molded product, and silver streak is generated on the surface of the molded product, so that the appearance quality of the molded product becomes poor. Further, in the molded product of Comparative Example 3, since the valve opening degree of the rotary valve 20 is set to 30%, the heat generation amount of shearing heat generated in the molten resin is large, and the molten resin is stored in the cavity 18. Foams,
The portion of the molten resin that is in contact with the inner wall surface of the mold 13, that is, the portion that forms the skin layer of the molded product, is instantly cooled and solidified and hardly foams. Therefore, a molded product having a relatively good appearance quality can be obtained. However, since the skin layer is slightly foamed, the molded product cannot sufficiently satisfy the requirements for appearance quality.

(Second Embodiment) In the second embodiment, the injection pressure of the injection molding machine 11 is set to a normal injection molding condition and the valve opening of the rotary valve 20 is set to 50%, and the injection molding is performed. A case will be described in which the heat generation amount of shear heat generation is controlled by adjusting the injection speed of the machine 11.

First, as in the first embodiment, the mold 13 is closed by a known means so that the cavity volume of the cavity 18 becomes the desired volume of the molded product.

Next, the drive controller 23 sets the injection speed of the injection molding machine 11 to, for example, 30% of the normal injection molding conditions, and injects the molten resin containing the foaming agent from the cylinder 15 into the cavity 18. Fill. At this time, since the injection speed is set to 30%, the heat generation amount of the shearing heat generated in the molten resin in the flow path 17 becomes small, and the molten resin does not foam in the cavity 18.
Thus, a dense skin layer of the molded product is formed by the molten resin that does not foam.

Next, the cavity 18 filled with the molten resin that is not foamed is injected and filled from the cylinder 15 while the injection speed is set to 70% of the normal injection molding condition by the drive control device 23. To do. At this time, since the injection speed is set to 70%, the heat generation amount of the shearing heat generated in the molten resin in the flow path 17 becomes large, and the shearing heat generation causes the foaming agent added to the molten resin. Is thermally decomposed, and the molten resin is foamed in the cavity 18 by the thermal decomposition of the foaming agent. Thus, the foamed molten resin forms the core of the molded article. Since the heat generation amount of the shearing heat generated in the molten resin in the flow path by appropriately setting the injection speed changes depending on the type of the molten resin passing through the flow path, the valve opening of the rotary valve, etc. It is necessary to obtain data on the amount of heat generation in advance and determine the set temperature of the cylinder based on the data.

Next, the injection speed is set to 30% again by the drive controller 23 in the cavity 18 in which the molten resin that does not foam and the molten resin that forms the core are injected and filled. While cylinder 15
Further, the molten resin is injected and filled. At this time, since the injection speed is set to 30%, the heat generation amount of the shearing heat generated in the molten resin in the flow path 17 becomes small, and the molten resin does not foam in the cavity 18. In this way, the foamed molten resin forming the core is covered with the molten resin that does not foam, and the molten resin having a volume corresponding to the intended volume of the molded product is formed in the cavity 1.
It will be injection-filled in 8.

Then, similarly to the first embodiment, the molded product made of the molten resin is separated from the mold 13.

A molded product (Example 2) molded by using the injection molding machine 11 in the second embodiment, and molded by using the injection molding machine 11 while changing the injection speed of the injection molding machine 11. Table 2 shows molding conditions and evaluation results for the molded products (Comparative Examples 4 and 5). The arrow (→) in the injection speed in Table 2 indicates that the setting of the injection speed is changed.

[0036]

[Table 2]

As can be seen from these evaluation results, in the molded product of Example 2, when the injection speed of the injection molding machine 11 was set to 70%, the molten resin containing the foaming agent passing through the rotary valve 20 was added. The amount of heat generated by shearing heat is increased, and the molten resin is heated to over 50 ° C. As a result, the foaming agent is thermally decomposed and the molten resin foams in the cavity 18. In the molded product of Example 2, first, the injection speed was set to 30% to form a dense skin layer by the molten resin, and then the injection speed was set to 70% to set the injection speed to 70%. Because the core is made of molten resin,
The skin layer is pressed against the inner wall surface of the mold 13 by the foaming pressure of the core. And again, the injection speed is 30%
Is set to cover the core with the molten resin. In this way, a foam-molded article without a sink mark and having an improved appearance quality can be obtained.

On the other hand, in the molded article of Comparative Example 4, since the injection speed is fixed at 30%, the amount of shearing heat generated in the molten resin is small, and the molten resin is kept inside the cavity 18. Does not foam. Therefore, in this molded product, a fine skin layer without silver streaks is formed, but a sink mark is generated, so that the appearance quality is poor. Further, in the molded product of Comparative Example 5, the injection speed was 70%.
%, The amount of heat generated by shearing heat generated in the molten resin is large and the molten resin is
Although foaming occurs inside, the portion of the molten resin that is in contact with the inner wall surface of the mold 13, that is, the portion that constitutes the skin layer of the molded product, is instantly cooled and solidified and hardly foams. Therefore, a molded product having a relatively good appearance quality can be obtained. However, since the skin layer is slightly foamed, the molded product cannot sufficiently satisfy the requirements for appearance quality.

After performing the step of forming the skin layer of the molded article by controlling the heat generation amount of the shear heat generation to be small, the molding is performed by controlling the heat generation amount of the shear heat generation to be large, for example. By performing the process of forming the core of the product or the process of controlling it so that the heat generation amount of the product is reduced a plurality of times in sequence while controlling the timing, it is possible to place the product at a predetermined location according to the shape and application of the product. The foamed molten resin can be allowed to be present, so that the occurrence of sink marks or the like at a predetermined portion of the molded product can be suppressed.

The heat generation amount of the shear heat generation can be controlled by adjusting the injection pressure of the injection molding machine, and the valve opening of the rotary valve, the injection pressure of the injection molding machine, and the injection speed can be adjusted. Also by combining them, the heat generation amount of the shear heat generation can be controlled. For an injection molding machine not provided with a rotary valve, the heat generation amount of the shear heat generation can be easily controlled by adjusting the injection pressure and / or the injection speed.

In each of the above-mentioned embodiments, when the appearance quality is not particularly required for the portion of the molded product corresponding to the vicinity of the gate portion 18a of the mold 13, the molded product with the core is It is not necessary to injection-fill the cavity 18 with molten resin that coats the core. Further, although the rotary valve 20 is used in order to generate shear heat generation in the molten resin in the flow passage 17, the present invention is not limited to this, and any valve capable of controlling the magnitude of flow passage resistance value can be used. Other valves can also be used. Also, although a double flight type is used as the screw,
A single flight type can also be used.
Moreover, although an ADCA-based foaming agent is used as a foaming agent,
It goes without saying that other foaming agents such as DNPT (N, N'-dinitrosopentamethylenetetramine) can be used.

[0042]

According to the present invention configured as described above, a dense skin layer of a molded product is formed by controlling the heat generation amount of shearing heat generation to be small at the initial stage of injection filling, and then the shearing heat treatment is performed. Since the core of the molded product is formed by controlling to increase the amount of heat generation, the skin layer is pressed against the inner wall surface of the mold by the foaming pressure of this core, and there is no sink mark, etc. An improved foam molded article can be obtained at low cost. Further, after performing the step of controlling to reduce the heat generation amount of the shear heat generation, for example, a step of controlling to increase the heat generation amount of the shear heat generation or a step of controlling to reduce the heat generation amount, By sequentially performing multiple times while controlling the timing,
The foamed molten resin can be made to exist in a predetermined portion of the molded product depending on the shape and use of the molded product, and thus it is possible to prevent the occurrence of sink marks or the like at the predetermined portion of the molded product.

Further, at least after the step of controlling to increase the heat generation amount of the shear heat generation is performed, the step of controlling to decrease the heat generation amount of the shear heat generation at the end of injection filling is performed. Can be covered with a molten resin that does not foam, and as a result, the core is not exposed on the surface of the molded product, and the appearance quality of this molded product can be further improved.

Further, since the heat generation amount of the shear heat generation with respect to the molten resin is controlled by using the flow path resistance of the rotary valve or the like, it is possible to suppress the increase in the apparatus cost of the injection molding machine. Further, since the heat generation amount of the shearing heat generation can be controlled by adjusting the injection pressure and / or the injection speed of the injection molding machine, it is possible to use the conventional injection molding machine having no rotary valve. Can be applied.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an injection molding machine to which a foam injection molding method according to the present invention is applied.

FIG. 2 is a graph showing a relationship between a valve opening degree and a temperature rise degree of a molten resin passing through the rotary valve in the rotary valve according to the present invention.

[Explanation of symbols]

 11 Injection Molding Machine 11a Injection Molding Machine Main Body 12 Nozzle Part 13 Mold 14 Injection Unit 15 Cylinder 16 Material Hopper 17 Flow Path (Molten Resin Supply Flow Path) 18 Cavity 19 Screw 20 Rotary Valve 21 Screw Rotation Motor 22 Base 23 Drive Control Device 24 Fixed mold 25 Intermediate mold 26 Movable mold 27 Compression cylinder 28 Piston rod 29 Return pin 30 Stopper

Claims (5)

[Claims] 1. When a molten resin, to which a foaming agent is added and which is melted at a temperature lower than the decomposition start temperature of the foaming agent, is injected and filled into the cavity of the mold, shear heat is generated in the molten resin. In the foaming injection molding method of thermally decomposing the foaming agent, the step of controlling to reduce the heat generation amount of the shear heat generation is performed at the initial stage of injection filling, and thereafter, at least the heat generation amount of the shear heat generation is performed. A foam injection molding method, characterized in that a step of controlling to increase the size is performed. 2. When the molten resin melted at a temperature lower than the decomposition starting temperature of the foaming agent is added to the cavity of the mold by injection, shearing heat is generated in the molten resin. In the foaming injection molding method of thermally decomposing the foaming agent, the step of controlling to reduce the heat generation amount of the shear heat generation is performed at the initial stage of injection filling, and thereafter, at least the heat generation amount of the shear heat generation is performed. A foam injection molding method, which comprises performing a step of controlling so as to increase and then performing a step of controlling so as to reduce the shear heat generation at the final stage of injection filling. 3. The control of the heat generation amount of the shear heat generation is performed by adjusting the flow passage area of the molten resin supply flow passage by the flow passage resistance provided in the molten resin supply flow passage. The foam injection molding method described. 4. The foam injection according to claim 1, wherein the heat generation amount of the shear heat generation is controlled by adjusting an injection pressure when the molten resin is injected and filled in the cavity. Molding method. 5. The foam injection according to claim 1, wherein the heat generation amount of the shear heat generation is controlled by adjusting an injection speed when the molten resin is injected and filled in the cavity. Molding method.